The present invention relates generally to security apparatus for information processing systems, and more particularly to the incremental delivery of authenticated access rights to an access control processor. The invention is particularly useful in connection with the secure transmission of premium television services via satellite or cable, but is not limited to such applications.
There are many schemes available for controlling access to electronic signals, such as those providing premium television services. Such schemes are necessary to maintain security, for example in subscription television systems such as cable television and satellite television systems. Typically, a system subscriber is provided with a decoder connected between a television signal source (e.g., cable feed or satellite receiver) and a television set. Each subscriber's decoder is remotely accessed by the system operator to enable or disable the receipt of specific services such as the Home Box Office (HBO) movie channel or special pay-per-view sports events. One problem with such systems is that "pirates" may attempt to break the system security and sell "black boxes" that enable the reception of all programming without paying for the services received. It has been difficult and expensive for system operators to contend with the piracy problem.
Various systems have been designed to make piracy more difficult. One such system is disclosed in U.S. Pat. No. 4,613,901 to Gilhousen, et al. entitled "Signal Encryption and Distribution System for Controlling Scrambling and Selective Remote Descrambling of Television Signals." In the Gilhousen, et al. scheme, various cryptographic keys are used to provide an encrypted television signal. Among the keys described are category keys, each common to a different subset of subscriber decoders. It is also known to provide program keys, in which each television program has a specific key associated therewith that is necessary to descramble or decrypt the particular program signal.
U.S. Pat. No. 5,115,467 to Esserman, et al. entitled "Signal Encryption Apparatus for Generating Common and Distinct Keys" also deals with the security issue. The generation of various different types of keys and their use is disclosed in the patent.
An example of a prior art communication system using encrypted category keys and program keys is the VideoCipher.RTM. II+ scrambling system produced and licensed by General Instrument Corporation of San Diego, Calif. to provide encrypted satellite television communication. The encrypted category key is derived from a category key, a unit key specific to a subscriber decoder, and access rights defining which services the particular subscriber is entitled to receive. The access rights are authenticated in the category key, which generally changes monthly.
In the VideoCipher II+ system, and other known systems, it has been necessary to provide the authenticated access rights with the encrypted category key in a single "category rekey" message. The access rights may be many bytes in length. Each category rekey message has a limited length. For example, category rekey messages in a particular system may be limited to two hundred bytes. Such limitations are typically required by the size of the buffer (e.g, RAM) which receives the message in the access control processor. If the number of bytes required to define access rights were to become too large, a single category rekey message could not hold the full description.
It would be advantageous to provide an access control system in which access rights can be delivered incrementally, in more than one category rekey message. It would be further advantageous to provide such a system that would operate even after only a partial set of access rights has been received. It would be still further advantageous to provide such a system that can receive partial sets of access rights in any order, without adversely affecting system operation.
The present invention Provides a system for incrementally delivering access rights having the aforementioned and other advantages.